The present invention relates to containers sealed with flexible lids formed from materials such as polymer film, aluminum foil, paper, and the like.
It is known to seal a container with a lid formed from a heavy-gauge aluminum foil having a heat-sealable material on its underside. The lid is shaped to include a cylindrical skirt that extends upwardly from an outer periphery of a center panel of the lid, such that the heat-sealable material is on the radially outwardly facing side of the skirt. The skirt is heat-sealed to a generally cylindrical inner surface of the container body adjacent the open end of the container, the center panel of the lid thus being recessed below a top edge of the container body. The lid includes a line of weakness such that the center panel can be torn free of the skirt, at least part of which remains attached to the container body. A pull tab is attached to the top surface of the center panel to aid the user in tearing out the center panel. The pull tab typically is heat-sealed to the center panel. For example, a container and lid generally as described above are disclosed in U.S. Pat. No. 4,744,484 to Grabher.
A difficulty associated with such container lids arises because of inevitable variations in the strength of the bond between the tab and the center panel. Such variations are due to mechanical process and material variations that are difficult to control or eliminate. Additionally, it has been found that the tab bond strength tends to diminish with aging of the lid. Accordingly, it can be expected that some proportion of the lids produced according to the conventional process will have a tab bond strength that is less than the force required to detach the center panel from the skirt. When the user pulls on the tab of such a lid, the tab will tend to come off the center panel and the user will then have to resort to other means to open the container, such as puncturing the lid with a sharp implement and then tearing out the lid in pieces. This is inconvenient for the user.